The compound cis-1-(3-chloro-2-propenyl)-3,5,7-triaza-1-azoniatricyclo(3.3.1.1.sup.3,7) decane chloride, known commercially as Dowicil 200 antimicrobial, is described in U.S. Pat. No. 3,228,829. Dowicil 200 antimicrobial possesses inherent instability problems. Also, various salts of the N-methyl analog of Dowicil 200 are known, i.e., the nitrate, chlorate, sulfate, rhodanide, metaborate, bichromate, perchlorate, ferrocyanate and picrate; U.S. Pat. No. 1,336,709. No utility is claimed for these latter compounds, however.